Cellular biology comprises a wide range of study involving a broad set of cellular processes. These processes include, but are not necessarily limited to, cellular growth, maintenance, metabolism, proliferation, differentiation, migration, as well as inter- and intracellular signaling pathways. These cellular processes are mediated by a wide variety of endogenous proteins and other ligands, for example hormones and other steroids. While these cellular processes are incredibly varied, the regulation of these cellular processes can ultimately be traced back to regulation of gene expression, and most commonly, but not necessarily, regulation of gene expression at the transcriptional level.
Gene expression is the process wherein the information contained in a particular gene is ultimately manifested in a protein, the mechanism of which is explained by the Central Dogma Theory (CDT). The CDT, first proposed by Francis Crick in 1956, is often considered the fundamental unifying theory of the life sciences and it states that the flow of genetic information, under ordinary conditions, goes from DNA to RNA via transcription, and then from RNA to protein via translation. Since then, scientists have discovered several processes that are exceptions, notably for example that of reverse transcription such as that undertaken by retroviruses, as well as several processes that are not explicitly covered in the CDT, such as forms of posttranslational modifications.
Gene expression is most commonly regulated at the transcriptional level and involves the alteration of transcription rates within a cell. Transcriptional regulation may include either transcriptional activation or transcriptional repression. Transcription of a gene requires the presence of RNA polymerase (RNAP) to proceed. RNAP can initiate transcription at specific DNA sequences known as promoters. Promoters are non-coding DNA sequences which are found near to and upstream of genes. Transcriptional regulation often involves the use of transcription factors (TFs), which are compounds that can bind to specific DNA sequences. TFs can function as an activator and thus promote transcription, or a repressor, and thus block transcription. Activators bind to DNA regions known as enhancers, and enhance the interactions between RNAP and promoters, thus increasing the rate of transcription. Repressors bind to DNA regions known as silencers, which are often located upstream of the target gene and near the promoter region. Repressors function to prevent the binding of RNAP to promoters and thus prevent transcription.
TFs that function as activators are comprised of two fundamental domains that function synergistically to activate gene expression: the DNA-binding domain (DBD) and the activation domain (AD). The DBD targets and binds to specific enhancer DNA sequences while the AD recruits proteins and RNAP to initiate and sustain transcription. TFs that function as repressors are likewise comprised of a DBD that similarly targets and binds to specific silencer DNA sequences. TFs that function as repressors may also be comprised of a repression domain (RD) are comprised of non-DNA binding proteins called corepressors. In eukaryotes, corepressors are proteins that bind to certain repressors in order to activate them, so that the repressor can bind to the silencer region and block transcription.
The field of nanotechnology has recently made great strides in contributing to therapeutic applications ranging from molecular imaging, stem cell differentiation, and drug delivery. There have been past attempts to create synthetic analogues of TFs for use in a wide variety of therapeutic applications. These synthetic analogues are called synthetic transcription factors (STFs). Further like endogenous TFs, STFs may act as either activators or repressors. Like TFs, STFs contain a DBD and either an AD if functioning as an activator and optionally an RD if functioning as a repressor. Activator STFs have been developed in the past by combining a DBD moiety such as zinc finger, oligonucleotides, and hairpin polyamide to an AD moiety such as wrenchnolol, peptoids, and peptides to induce gene expression. Repressor STFs have been developed in the past by combining a DBD moiety with RD moieties to repress gene expression.
STFs have a high binding affinity for DNA, they can exhibit specificity to bind to only certain sites such as enhancers or silencers, for example via tunable hairpin polyamides that complement targeted DNA sequences, and they possess a small molecular size. As such, STFs have significant potential therapeutic application. However, existing STFs suffer from a number of known problems that currently limit their potential therapeutic applications. STFs are known to have poor penetration of the nuclear membrane, which is significant because transcription occurs in the nucleus. STFs that cannot easily penetrate the nuclear membrane cannot effectively regulate transcription. Furthermore, STFs are often subject to intracellular degradation, thus limiting their effectiveness. Surprisingly, the current invention relating to biologically active synthetic nanoparticle constructs overcomes these limitations and provides effective compositions for use in regulating, mediating, or modifying biological activity and processes including gene expression and the cellular processes that rely on gene expression such as cellular proliferation, differentiation, and migration.